The invention relates to photostable cosmetic or pharmaceutical light screening compositions for the protection of the human epidermis or hair against ultraviolet rays of wavelengths between 280 and 400 nm (UV-A/UV-B).
More specifically, the invention relates to photostable light screening compositions containing a dibenzoylmethane UV-A screening agent and a p-methoxycinnamate UV-B screening agent wherein one of the screening agents is incorporated in a polymer latex.
U.S. Pat. No. 5,372,804 (Chesebrough-Pond) relates to cosmetic compositions having at least one light screening agent wherein the light screening agent, is carried in or on polymer latex particles. The polymer latex particles effect a good deposition of the light screening agents onto hair or skin. Specifically disclosed light screening agents include benzophenone compounds, dibenzoylmethane derivatives and cinnamate derivatives, such as 2-ethylhexyl p-methoxycinnamate (PARSOL(copyright) MCX). The polymer particles employed may be of any polymeric material that is a good film former. The polymer particles may be substantially solid or may be porous and have a particle size of about 10-1000 nm. In order to get polymers having good film forming characteristics, a low glass transition temperature in the region of the temperature of normal use of the cosmetic composition, approximately 30xc2x0 C., is required.
The above mentioned U.S. patent only discloses that light screening agents can be incorporated into a latex, thereby achieving the advantage of enhanced deposition. Said U.S. patent does not address the problem of photostability, which problem is due to an interaction of 4-tert. butyl-4xe2x80x2-methoxydibenzoyl-methane (PARSOL(copyright) 1789) with other light screening agents under light especially with 2-ethylhexyl p-methoxycinnamate (PARSOL(copyright) MCX).
Cosmetic light screening compositions based on dibenzoyl methane derivatives as UV-A screening agent and photostabilized with 3,3-diphenylacrylate derivatives are described in the European Patent Publication EP 0 514 491 B1 and in the European Publication EP 0 780 119 A1. However, this type of stabilization does not prevent the photochemical interaction between cinnamate derivatives, such as 2-ethylhexyl p-methoxycinnamate, and dibenzoylmethane derivatives, such as 4-tert. butyl-4xe2x80x2-methoxydibenzoyl-methane.
It has now been found that the photostability of light screening compositions containing a dibenzoyl methane UV-A screening agent and a p-methoxycinnamate UV-B screening agent is improved if one of said light screening agents is incorporated into a polymer latex.
Accordingly, one aspect the invention is concerned with a method of photostabilizing mixtures of a dibenzoylmethane UV-A screening agent and a p-methoxycinnamate UV-B screening agent in a light screening composition, which method comprises incorporating one of said light screening agents into a polymer latex.
In still another aspect the present invention is concerned with a light screening composition containing, based on the total weight of the composition,
about 0.5 wt % to about 5 wt % of a dibenzoylmethane UV-A screening agent incorporated into a polymer latex,
about 1 wt % to about 15 wt % of a p-methoxycinnamate UV-B screening agent; and,
optionally, other conventional UV-A and UV-B screening agents.
In yet another aspect the present invention is concerned with a light screening composition containing, based on the total weight of the composition,
about 1 wt % to about 15 wt % of p-methoxycinnamate UV-B screening agent incorporated into a polymer latex;
about 0.5 wt % to about 5 wt % of a dibenzoylmethane UV-A screening agent; and,
optionally, other conventional UV-A and UV-B screening agents.
As far as the dibenzoylmethane UV-A screening agent is concerned, the preferred compound is 4-tert. butyl-4xe2x80x2-methoxydibenzoyl-methane, which is sold under the tradename PARSOL(copyright) 1789.
Other suitable compounds of this particular type include: 2-methyldibenzoyl-methane, 4-methyldibenzoyl-methane, 4-isopropyldibenzoyl-methane, 4-tert. butyldibenzoyl-methane, 2,4-dimethyldibenzoyl-methane, 2,5-dimethyldibenzoyl-methane, 4,4xe2x80x2-diisopropyldibenzoyl-methane, 2-methyl-5-isopropyl-4xe2x80x2-methoxydibenzoyl-methane, 2-methyl-5-tert. butyl-4xe2x80x2-methoxydibenzoyl-methane, 2,4-dimethyl-4xe2x80x2-methoxydibenzoyl-methane, and 2,6-dimethyl-4-tert. butyl-4xe2x80x2-methoxydibenzoyl-methane.
As used herein the term xe2x80x9cp-methoxycinnamate UV-B screening agentxe2x80x9d refers to compounds such as 2-ethoxyethyl p-methoxycinnamate, 2-ethylhexyl (or pentyl) p-methoxy-cinnamate, potassium p-methoxycinnamate, sodium p-methoxycinnamate, ammonium p-methoxycinnamate, salts of primary, secondary or tertiary amines of p-methoxycinnamic acid like mono-, di-, tri-ethanol amine salt and the like. Preferred is 2-ethylhexyl p-methoxycinnamate, sold under the tradename PARSOL(copyright) MCX.
As used herein, the term xe2x80x9cpolymer latexxe2x80x9d refers to a stable colloidal dispersion of polymer particles in an aqueous or an aqueous based phase including polymers and/or copolymers of unifunctional monomers and/or multifunctional monomers. The dibenzoylmethane UV-A screening agent or the p-methoxycinnamate UV-B screening agent is incorporated into the polymer latex.
As used herein the term xe2x80x9cunifunctional monomersxe2x80x9d includes C1-C6-alkyl (meth)acrylate, acrylic acid, methacrylic acid, styrene, ethylene, propylene, butylene, butadiene, isoprene, isobornyl methacrylate (IBOMA), trifluoroethyl methacrylate, perfluoralkyl 2-ethylacrylate and the like.
As used herein the term xe2x80x9cmultifunctional monomersxe2x80x9d includes allyl methacrylate (ALMA), ethyleneglycol dimethacrylate (EGDMA) and the like.
A preferred polymer latex is a stable colloidal dispersion of copolymer particles of methyl methacrylate (MMA) and acrylic acid (AA) crosslinked with allyl methacrylate (ALMA) and ethyleneglycol dimethacrylate (EGDMA) or containing isobornyl methacrylate (IBOMA) crosslinked with allyl methacrylate (ALMA).
The polymer particles can have a matrix structure within which the dibenzoyl-methane UV-A screening agent or the p-methoxycinnamate UV-B screening agent is homogeneously distributed over the whole volume of the polymer particles, or the polymer particles can have a reservoir structure.
As used herein the term xe2x80x9creservoir structurexe2x80x9d refers to particles having a polymer core surrounded by a polymer shell, wherein the core contains the dibenzoylmethane UV-A screening agent or the p-methoxycinnamate UV-B screening agent.
In one aspect, the core and the shell portions of the core/shell polymer particles may have the same chemical composition with regard to the monomers used. Suitable monomers used include unifunctional and multifunctional monomers as listed above.
In another aspect, the core and shell portions of the core/shell polymer particles may differ in their chemical composition. In this case, the monomers used in the core portion of the core/shell particles may also include the unifunctional and multifunctional monomers as listed above. The monomers used in the shell portion of the core/shell particles suitably include hydrophilic or fluorinated monomers.
Preferred core/shell particles include particles wherein
a) the core consists of a polymer and/or a copolymer of methyl methacrylate (MMA) and acrylic acid (AA) crosslinked with allyl methacrylate (ALMA) and ethyleneglycol dimethacrylate (EGDMA) or containing isobornyl methacrylate (IBOMA) crosslinked with allyl methacrylate (ALMA); and
b) the shell consists of hydrophilic polymer or fluorinated polymer chains.
Hydrophilic polymer shells are obtainable by copolymerization of monomers containing carboxylic acid groups such as acrylic acid, methacrylic acid, monomers bearing hydroxyl groups, such as, e.g., hydroxy-C1-C6-alkyl (meth)acrylate, (HEMA) and acrylamides (AAm). A suitable hydroxy-C1-C6-alkyl (meth)acrylate is hydroxyethyl methacrylate.
Fluorinated polymer shells are obtainable by copolymerization of acrylic esters, such as, e.g., methyl methacrylate (MMA) or isobornyl methacrylate (IBOMA) with fluorinated monomers, such as, e.g., trifluorethy methacrylate (TRIFEMA) or perfluoroalkyl 2-ethylacrylate (PF2EA).
The core can be surrounded by a single shell or by two or more shells, whereby the first shell surrounding the core and the following shell may be formed of the same polymer particles or of different polymer particles. For example, the first shell may be formed of a hydrophilic polymer and the following shell may be formed of a fluorinated polymer and vice versa.
If core and shell are not formed of the same polymer particles, a two component core-shell polymer is obtained having various morphological structures as described by Chen et al., Macromolecules 1991, 24, 3779-3787.
The polymer particles as defined above have a glass transition temperature between about 50xc2x0 C. and about 100xc2x0 C. The glass transition temperature can be adjusted to a given value by choosing the initial content of each monomer and by crosslinking with the above mentioned multifunctional monomers. Generally, a higher content of cross-linking agent increases the glass transition temperature, while increased alkyl chain lenghts in acrylate monomers result in lower glass transition temperatures of the polymer latex. Further, the glass transition temperature of the polymer latex will be lowered by increased levels of the incorporated screening agent, e.g., PARSOL(copyright) 1789.
The glass transition temperature of the polymer particles used for the core portion may be the same or different compared to the glass transition temperature of polymer particles used for the shell portion.
The polymer latex containing polymer particles having the dibenzoylmethane UV-A screening agent or the p-methoxycinnamate UV-B screening agent incorporated into the latex can be produced by emulsion polymerization including a crosslinking procedure. Thus, polymer particles having a glass transition temperature  greater than 50xc2x0 C., preferably  greater than 70xc2x0 C. are obtained.
The glass transition temperature is important since the polymer particles must be in a glassy state at storage temperature to impart a high stability and tightness to the system.
The preparation of latex polymers by emulsion polymerization has long been known. For example, U.S. Pat. No. 5,189,107 discloses that latex polymers having uniform particle size can be obtained by using latex seeds in the polymerization reaction to better control the particle size distribution.
Thus, the invention also comprises a process for the preparation of polymer particles having a matrix structure within which a dibenzoylmethane UV-A-screening agent or a p-methoxycinnamate UV-B screening agent is homogeneously distributed over the whole volume of the particles by
a) dissolving the dibenzoylmethane UV-A screening agent or the p-methoxycinnamate UV-B screening agent in a blend of monomers;
b) pre-emulsifying the solution of step a) in an aqueous solution containing an emulsifier;
c1) continuously introducing the pre-emulsion of step b) into a reactor containing an aqueous initiator solution or
c2) introducing a small amount of the pre-emulsion of step b) into a reactor containing an aqueous initiator solution thus, obtaining seed polymer particles and then continuously introducing the remaining pre-emulsion.
The temperature in the reactor of step c1 or c2 is from about 70xc2x0 C. to about 90xc2x0 C., preferably about 80xc2x0 C.
The latex obtained by the above described emulsion polymerization process exhibits a colloidal dispersion of polymer particles having a matrix structure, within which the dibenzoylmethane UV-A screening agent or the p-methoxycinnamate UV-B screening agent is homogeneously distributed over the whole volume of the particles.
A latex containing polymer particles having a reservoir structure can be prepared by a two step emulsion polymerization process having a first step polymerization to obtain the core polymer particles and a second step polymerization to obtain polymer particles having at least one shell surrounding the core.
The first polymerization step can be carried out as described above in steps a), b), c1) and c2).
The second polymerization step includes another emulsion polymerization that is carried out according to steps b), c1) and c2) in the presence of the latex prepared in the first polymerization step and in the absence of light screening agents, using the same or different monomers as used in the first step.
In one embodiment of the invention, the second polymerization step includes adding monomers containing carboxylic acid groups such as acrylic acid, methacrylic acid (MAA), monomers bearing hydroxyl groups, such as, e.g., hydroxy-C1-C6-alkyl (meth)acrylate, (HEMA) and acrylamides (AMD).
In another embodiment of the invention, the second polymerization step includes adding monomers containing acrylic esters, such as, e.g., methyl methacrylate (MMA) or isobornyl methacrylate (IBOMA) and fluorinated monomers, such as, e.g., trifluoroethyl methacrylate (TRIFEMA) or perfluoroalkyl 2-ethylacrylate (PF2EA).
The core/shell particles of the present invention can also be prepared by an inverted core/shell polymerization process, in which the shell portion is prepared first, followed by polymerization of the core monomer in the presence of the shell materials.
The weight ratio of the core portion to shell portion is suitably from about 1 to 10.
Suitable emulsifiers are anionic and nonionic surfactants, preferably anionic surfactants.
Conventional anionic surfactants, such as, e.g., alkyl sulfates, alkyl ether sulfates, alkyl succinates, alkyl sulfosuccinates, alkyl phosphates, alkyl ether phosphates, alkyl ether carboxylates, especially their sodium, magnesium, ammonium and mono-, di- and triethanolamine salts can be used. The alkyl groups generally contain from 8 to 18 carbon atoms and may be unsaturated, i.e. C8-18-alkenyl groups also come into question as replacements for the alkyl groups in such anionic surfactants.
Suitable anionic surfactants may also be sorbitan derivatives sold under the tradename TWEEN by ICI Americas Incorporated, Wilmington. Preferred are polyoxyethylene-sorbitan-fatty acid esters, such as, e.g., polyoxyethylene(20)sorbitan monolaurate, which is commercialized under the tradename TWEEN 20 (ICI Chemicals).
Another suitable and preferred surfactant is ABEX(copyright) 3594 (Rhone-Poulenc) or DOWFAX(copyright) 8390 (Dow Chemical).
As used herein the term xe2x80x9cinitiator solutionxe2x80x9d refers to an aqueous solution of peroxides, perphosphates, percarbonates, persulfates, organic peroxides, and salts thereof. Preferred is ammonium persulfate.
The polymer particles have a particle size of about 100 nm to about 500 nm, preferably about 100 nm to about 400 nm, more preferably about 250 nm to about 350 nm.
Where convenient the light screening composition of the present invention may further include other conventional UV-A and UV-B screening agents.
The term xe2x80x9cconventional UV-B screening agentsxe2x80x9d, i.e., substances having absorption maxima between about 290 and 320 nm, refers to the following UV-B screening agents:
Acrylates, such as 2-ethylhexyl 2-cyano-3,3-diphenylacrylate (octocrylene, PARSOL(copyright) 340), ethyl 2-cyano-3,3-diphenylacrylate and the like;
Camphor derivatives, such as methyl benzylidene camphor (PARSOL(copyright) 5000), 3-benzylidene camphor, camphor benzalkonium methosulfate, polyacrylamidomethyl benzylidene camphor, sulfo benzylidene camphor, sulphomethyl benzylidene camphor, therephthalidene dicamphor sulfonic acid and the like;
Organosiloxane compounds containing benzomalonate groups as described in the European Patent Publications EP 0358584 B1, EP 0538431 B1 and the European Publications EP 0709080 A1 and EP 0897716 A2.
Pigments, such as microparticulated TiO2, and the like. The term xe2x80x9cmicroparticulatedxe2x80x9d refers to a particle size from about 5 nm to about 200 nm, particularly from about 15 nm to about 100 nm. The TiO2 particles may also be coated by metal oxides, such as, e.g., aluminum or zirconium oxides, or by organic coatings, such as, e.g., polyols, methicone, aluminum stearate, alkyl silane. Such coatings are well known in the art.
Imidazole derivatives, such as, e.g., 2-phenylbenzimidazole-5-sulfonic acid and its salts (PARSOL(copyright) HS). Salts of 2-phenylbenzimidazole-5-sulfonic acid are, e.g., alkali salts, such as sodium- or potassium salts, ammonium salts, morpholine salts, salts of primary, sec. and tert.amines like monoethanolamine salts, diethanolamine salts and the like.
Salicylate derivatives, such as isopropylbenzyl salicylate, benzyl salicylate, butyl salicylate, octyl salicylate (NEO HELIOPAN OS), isooctyl salicylate or homomenthyl salicylate (homosalate, HELIOPAN) and the like;
Triazone derivatives, such as octyl triazone (UVINUL T-150), dioctyl butamido triazone (UVASORB HEB) and the like.
The term xe2x80x9cconventional UV-A screening agentsxe2x80x9d, i.e., substances having absorption maxima between about 320 and 400 nm, refers to the following UV-A screening agents:
Dibenzoylmethane derivatives, such as 4-tert. butyl-4xe2x80x2-methoxydibenzoyl-methane (PARSOL(copyright) 1789), dimethoxydibenzoyl-methane, isopropyldibenzoyl-methane and the like;
Benzotriazole derivatives, such as 2,2xe2x80x2-methylene-bis-(6-(2H-benzotriazole-2-yl)-4-(1,1,3,3-tetramethylbutyl)-phenol) (TINOSORB M) and the like;
Triazine derivatives, such as 2,4-bis-[4-(2-ethyl-hexyloxy)-2-hydroxy-phenyl]-6-(4-methoxyphenyl)-1,3,5-triazine; available under the tradename TINOSORB S from Ciba Speciality Chemicals Holding Switzerland; and
Pigments, such as microparticulated ZnO and the like. The term xe2x80x9cmicro-particulatedxe2x80x9d refers to a particle size from about 5 nm to about 200 nm, particularly from about 15 nm to about 100 nm. The ZnO particles may also be coated by metal oxides, such as, e.g., aluminum or zirconium oxides, or by organic coatings, such as, e.g., polyols, methicone, aluminum stearate, alkyl silane. Such coatings are well known in the art.
Suitable organosiloxane compounds are those described in general in the European Patent EP 0538431 B1, namely compounds of the general formula I, 
wherein
R signifies C1-6-alkyl or phenyl;
A signifies a group of the formula IIa and/or IIb; 
wherein
R1 and R2 each independently signify hydrogen, hydroxy, C1-6-alkyl or C1-6-alkoxy;
R3 signifies C1-6-alkyl;
R signifies hydrogen or C1-6-alkyl;
R5 and R6 each independently signify hydrogen or C1-6-alkyl;
r has a value of from 0 to 250;
s has a value of from 1 to 20;
r+s has a value of at least 3; and
n has a value from 1 to 6.
The term xe2x80x9cC1-6-alkylxe2x80x9d refers to groups such as methyl, ethyl, propyl, isopropyl, butyl, sec. butyl, isobutyl, pentyl, and neopentyl.
The term xe2x80x9cC1-6-alkoxyxe2x80x9d refers to the corresponding alkoxy groups.
The residues R are preferably methyl.
The residues R1 and R2 are preferably hydrogen, methoxy or ethoxy, more preferably hydrogen, or one of R1 and R2 is hydrogen and the other is methyl, methoxy or ethoxy.
The residues R3 are preferably methyl or ethyl, more preferably ethyl.
Preferably, R4 is hydrogen or methyl, R5 and R6 are hydrogen and n is 1.
Among the above described organosiloxanes, the following organosiloxane compound of the general formula I described in the European Patent Publication EP 0709080 A1 and hereinafter referred to as xe2x80x9cPolysiloxane Axe2x80x9d is preferred. Polysiloxane A is a compound of the above formula I, wherein
R signifies methyl;
A signifies a group of the formula IIaa and/or Iibb: 
xe2x80x83r is a statistical mean of about 4; and
s is a statistical mean of about 60.
In case A signifies a group of the formula (IIa and IIb) or of the formula (IIaa and IIbb) respectively, the ratio of polysiloxane units having a chromophore residue A of the formula IIa or IIaa respectively, to those having a chromophore residue A of the formula IIb or IIbb respectively, is not critical.
Other suitable organosilioxane compounds are those described in the European Patent EP 0358584 B1, namely, e.g., compounds of the general formula I wherein
R signifies methyl;
A signifies a group of the formula IIc 
wherein R1-R6 and n are as described above.
The preparation of novel light screening compositions, especially of preparations for skin protection and, respectively, sunscreen preparations for everyday cosmetics is well known to the skilled artisan in this field and comprises incorporating the polymer latex containing the dibenzoylmethane UV-A screening agent or the p-methoxycinnamate UV-B screening agent optionally together with other conventional UV-B screening agents and/or conventional UV-A screening agents as described above in a cosmetic base which is usual for light screening agents.
In a cosmetic composition of the present invention, the polymer latex particles act as carrier for the dibenzoylmethane UV-A screening agent or for the p-methoxycinnamate UV-B screening agent.
The solid content of polymer particles in the latex is suitably from about 10 wt % to about 50 wt %.
The latex contains the dibenzoylmethane UV-A screening agent in an amount of from about 5 wt % to about 30 wt %, preferably from about 5 wt % to about 15 wt %, more preferably from about 6 wt % to about 10 wt %, or the latex contains the p-methoxycinnamate UV-B screening agent in an amount of from about 1 wt % to about 15 wt %, preferably from about 2 wt % to about 8 wt %, more preferably about 5 wt %.
The amount of conventional UV-B screening agents and/or conventional UV-A screening agents is not critical. Suitable amounts include, but are not limited to:
xe2x80x9cPolysiloxane Axe2x80x9d: about 0.5 to about 15 wt %,
PARSOL(copyright) 340: about 0.5 to about 10 wt %,
PARSOL(copyright) 5000: about 0.5 to about 4 wt %,
PARSOL(copyright) HS about 0.5 to about 10 wt %
TINOSORB M: about 0.5 to about 10 wt %,
TiO2: about 0.5 to about 25 wt %,
ZnO: about 0.5 to about 20 wt %.
The light screening compositions of the present invention can be used as cosmetic or pharmaceutical formulations. The term xe2x80x9ccosmeticxe2x80x9d as used herein denotes topical formulations that are intended for the maintenance, improvement, or restoration of skin and hair. The term xe2x80x9cpharmaceuticalxe2x80x9d as used herein denotes topical formulations that are intended for therapy and prophylaxis of diseases and includes formulations that contain active ingredients that exert a medicinal effect.
The compositions of this invention take the form of a lotion, a gel, a solid stick, an emulsion, e.g., cream, milk, or of a vesicular dispersion of ionic or nonionic amphiphilic lipids, an aerosol, a spray, a foam, a powder, a shampoo, a hair conditioner or lacquer or a make-up, etc. See also, Sunscreens, Development, Evaluation and Regulatory Aspects, eds. Lowe, N. A.; Shaath, M. A.; (Marcel Dekker, Inc.) New York and Basel, 1990.
The usual excipients and auxiliary agents known to the skilled practitioner can be used for the preparation of these forms, e.g., oils, waxes, alcohols, polyols, etc., particularly fatty acids, esters, fatty alcohols, but also ethanol, isopropanol, propylene glycol, glycerine, etc.
The formulations may contain further adjuvants, e.g., further solvents, thickeners, emollients, emulsifiers, humectants, tensides, preservatives, antifoams, fragrances, oils, waxes, lower polyols and monohydric alcohols, propellants, silicones, colourings and pigments, etc.
For protection of the hair, the suitable formulations are shampoos, conditioners, lotions, gels, emulsions, dispersions, lacquers, etc.
The preparation of all these formulations is well known to the skilled artisan in this field.